The present invention relates to a method of producing workpieces and objects fabricated from materials including non-corrosion-resistant metals and metal alloys which are coated with wear-resistant, non-metallic coatings of nitrides, carbides, borides, oxides or silicides of elements of the fourth to the sixth b subgroup of the Periodic Table of Elements and in which a corrosion-resistant intermediate layer is arranged between the workpiece surface and the wear-resistant, non-metallic coating. In another aspect, the present invention relates to the articles having improved properties.
Workpieces and objects formed of metals and metal alloys exhibiting little resistance to corrosion are increasingly provided for technical and decorative applications with hard, wear-resistant and in some instances also decorative coatings of nitrides, carbides, borides, oxides and silicides of elements of the fourth to the sixth b subgroup of the periodic table such as e.g. titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum or tungsten. The application of these coatings takes place in accordance with the so-called PVD method (physical vapor deposition) which is well known in the art (see, for example, Kirk-Other's Encyclopedia of Chemical Technology, Third Edition, Volume 20, pages 42-47 and Volume 23, pages 295-299; these excerpts are entirely incorporated herein by reference). Coatings of titanium nitride and titanium carbide are preferred. As used herein, the expression "PVD" coating or layer is intended to refer to these known coatings or claddings.
However, the coatings produced in this manner have the disadvantage that they are brittle, porous and form microcracks. These layers exhibit a high so-called pinhole density due to their columnar growth. As a result, they do not offer good corrosion protection for the material thereunder, especially since these layers behave in an electrochemically inert manner so that the baser substrata are corrosively dissolved.
DE 38 09 139 (GB 2,218,111) teaches the arranging of a corrosion-resistant, dense layer of a palladium-nickel alloy between the workpiece surface and the PVD coating. This layer prevents the attack of corrosion through the porous PVD coating of the non-corrosion-resistant material of the foundation. In addition, a palladium-nickel layer has the advantage that it is almost as noble as the PVD layer and is therefore also barely attacked electrochemically. However, such layers have the disadvantage that they contain nickel which can act as an initiator of allergies. Palladium can also initiate allergies in some instances. Thus there was a need to avoid nickel and, if possible, palladium as alloy components for objects and workpieces which can come in contact with human skin.
DE 42 17 612, which is not a prior publication, describes metallic workpieces and their production which are provided with a corrosion-resistant underlayer of copper-tin alloys and with a wear-resistant upper layer consisting of metals such as chromium steel, molybdenum or manganese, or oxides, carbides or materials containing other hard substances. They are applied exclusively by means of thermal spraying methods such as flame spraying.
The use of galvanically applied copper-tin alloys as corrosion-resistant coatings is also known from "Ullmanns Encyklopadie der Technischen Chemie", 4th edition, volume 12, pages 190-194.